The present invention relates to a tube emitting electromagnetic radiation, made of a transparent non-fluorescent material, in particular a glass-based or quartz-based material, and having a straight structure drilled from end to end by a bore elongate around an axis so as to confine a housing designed to contain a radiation-emitting filament or plasma bundle.
It also relates to a device and a method implementing such a tube.
The invention finds a particularly important, although non-exclusive, application in the field of photochemical treatment of materials by ultraviolet radiation with emitting tubes containing an ionized gas, the pressure of which gas depends on the concentration of plasma inside the tube, used for example in the sterilization field, the paper industry, textiles, the wood and plastic materials industry, the food industry, the automobile industry and the printing field, in particular for polymerization of inks or varnishes on films, for example formed by supports in the form of reels of paper or cardboard, or supports made of metallic material such as aluminium or copper foil or steel strip, or supports made from synthetic material such as plastic products, PVC, polyethylene or other, or supports made of natural, recomposed or synthetic wood, or even electronic circuitry or any other support.
Another application is in the infrared field.
The invention is not limited to the types of products to be treated. It can for example be used for drying of products in plate form, for drying of certain varnishes and adhesives, for drying of wire-based products extending elongate around an axis, or for sterilization of liquid products in the form of a sheet or of a column around an axis.
Glass tubes emitting ultraviolet or infrared rays comprising a cylindrical bore are already known. These tubes in general associated to concave reflectors of parabolic or elliptic cross sections present drawbacks. They present large dimensions, are cumbersome and are not of optimum efficiency.
Most devices of the prior art in fact essentially describe separate emitters/reflectors implementing a distribution of the radiation emitted by a bundle or a filament according to two embodiments, i.e. primary rays which are emitted from the source in a divergent flux, and secondary rays which, being emitted from the source, are reflected on a surface presenting a cross section in the form of a mathematical curve to reach the irradiated plane in a convergent or parallel flux.
In all cases, and by structural defect of the system, the primary rays therefore do not have the same optimized trajectory, and consequently the same efficiency, as the secondary rays.
The document U.S. Pat. No. 3,885,181 describes a high-pressure sodium lighting lamp designed to emit rays in the visible field. It comprises a tubular discharge enclosure, made of an alumina-charged polycrystalline material. It has a non-circular cross section for an asymmetric polar distribution of the light emitted by the lamp. The emitting source is diffused from a luminous surface, and its plasma section is imposed by the internal geometry of the enclosure. The radiating source is not pin-point and the lamp is not equipped with a reflector or a monoblock emitter/reflector. Such a lamp is used for public lighting or for traffic signals.
The document U.S. Pat. No. 2,254,962 relates to an optic device composed of a cylindrical lens having a central refraction surface and a reflector with additional elliptic reflection and refraction surfaces of the same virtual focal spot. The light source is distinct and is housed in a semi-open notch, being dissociated from the reflector, which cannot restitute the whole of the radiation. The walls of the notch are arranged in such a way as to obtain divergent fluxes in the lens when passing the dioptric planes formed by the edges forming the confines of the notch. Such a device does not constitute a longitudinal monoblock emitter/reflector able to recover the whole of the emitted radiation over 360xc2x0.
The object of the present invention is to provide a radiation-emitting tube, a device and a method implementing such a tube, meeting the requirements of practice better than those known in the prior art.
A first object of the invention is to achieve a compact tube which is not cumbersome, able to render the primary and secondary rays homogeneous, complementary, and directed in the same direction towards the irradiated product, in order to optimize the usable photochemical, photothermal and/or photoluminous radiating energy.
A second object of the invention consists in recovering the whole of the spatial radiation emitted by an electromagnetic emitting tube to increase the focusing and the energy efficiency.
The invention stems from the idea of giving the bore an appreciably square or rectangular cross section, at least two opposite sides of which are of a cross section in the form of a convex curve, so as to obtain parallel fluxes when passing the dioptric planes formed by said sides.
What must be understood here by convex is an internal convex curve whose peak is directed towards the axis of the bore.
What must be understood here by appreciably square or rectangular is a four-sided figure inscribed in a square or a rectangle, said sides being in an arc of a circle with large radii of curvature, i.e. for example R greater than 10 mm.
To do this the centre of the plasma bundle, or the irradiating filament, is arranged to be at the centre of the geometric optics of said dioptric surfaces.
Thus the convex dioptric surfaces of the bore modify the divergent radiating flux from the geometric centre of the convex curves to form a flux which is parallel or appreciably parallel, in the transparent solid medium, then parallel or even convergent towards the plane to be irradiated, in combination with the dioptric output surface of the tube and/or a reflecting surface of the emitted rays situated on the side walls, on each side, for example symmetrically with respect to the axial plane of the bore.
The tube according to the invention is characterized in that the bore is of appreciably square or rectangular shaped cross section at least two opposite sides of which are in the shape of convex curves, said sides forming dioptric surfaces arranged to modify the direction of the rays emitted from the filament or from the axis of the emitting bundle to make them parallel or appreciably parallel in the transparent solid medium of the glass.
By obtaining parallel rays in the transparent medium, subsequent treatment of the rays is rendered considerably easier. Proliferation of the rays is also reduced achieving in particular an excellent power density in the case of focusing, and enabling limiting of the divergent rays to be achieved in the case of parallel flux irradiation.
In an advantageous case, the sides of the bore are respectively symmetrical with respect to the planes of symmetry of the square or of the rectangle, the direction of the rays being appreciably parallel to that of a plane of symmetry of the square or of the rectangle of the bore.
In the embodiments more particularly described, the present invention implements a straight emitting tube whose geometric centre of emission is merged with and identical to the focal spot of a corresponding reflector, which is also straight and of at least partially flat or appreciably flat cross section to treat flat surfaces, or of at least partially inverted parabolic cross section to focus the radiation, the generating line at the peak of the curve of the reflector being parallel to the axis which is merged with and identical to the focal line, and the end edges of the straight or inverted parabolic portions being situated below the axis of the bore, on the other side of the latter with respect to said generating line at the peak.
By inverted parabola we mean the reflection curve which transforms the parallel flux into a convergent flux focused on a line.
More precisely the ultraviolet, and/or visible, and/or infrared radiation emitters of the invention more particularly described here are tubes comprising electrodes at very high temperature (greater than 1000xc2x0 C.) called hot electrodes generating a plasma arc with continuous or discontinuous photon emission.
The electric arc generated by the two electrodes, respectively situated on each side of the transparent non-fluorescent tube, generates a luminous cylinder of constant cross section generally formed by one or more metallic iodides in the plasma state, or by xenon or a mercury/xenon mixture or other gases or rare earths.
The luminous cylinder presents a total length constituted by the distance between the two electrodes, for example comprised between a few mm for short arc emitters and more generally between 30 mm and 2500 mm, or even several meters, for example ten or fifteen meters, and also presents a cross section of the luminous zone with high plasma concentration smaller than the internal cross section of the transparent tube which contains it.
A voltage between electrodes comprised between 20 volts/cm and 150 volts/cm, for example 30 volts/cm or 100 volts/cm results in fact in an extremely reduced appreciably cylindrical bundle cross section forming a luminous pencil beam appearing as being completely away from the walls of the bore, creating a space of a relative vacuum which generates a reduced pressure appreciably equal to atmospheric pressure at the level of the internal wall of the cylindrical tube or of the monoblock emitter/reflector tube.
Moreover, the plasma concentration fosters an electronic and plasmatic gaseous vacuum in the vicinity of the internal walls which slows down the heat transfer to the outside, resulting in colder enclosure walls.
The metallic iodide(s) can originate from pure metals or alloys that is to say and for example a pure mercury, a pure iron, a pure gallium, an iron/cobalt (mixture), a gallium/lead (mixture), a mercury/gallium (mixture), etc.
The gas(es) used can be pure (for example xenon) or in mixture form (for example mercury/xenon), subjected as is known to frequencies other than 50 Hz, either of alternating current or of pulsed current or not, of constant polarity and variable intensity.
The list of mixtures of metals, rare earths and/or gases mentioned above is naturally not exhaustive. Moreover their respective proportions, and the choice of frequency, pulsing or modulation, are determined according to the specific wavelengths of the rays.
In advantageous embodiments recourse is more or less had to one and/or the other of the following arrangements:
the sides of the bore are arranged to form dioptric surfaces so as, in combination with the output dioptric surface of the tube or with a reflecting surface associated with the output dioptric surface of the tube, to direct the rays in a parallel or convergent flux towards a surface or a line to be irradiated;
the four sides of the bore are of convex shape, for example the opposite sides being identical two by two;
the convex shape of the internal walls of the bore is a portion of a circle whose radius of curvature is determined by a conventional calculation of the radius of curvature of thick biconvex lenses. For example, the radius of the circle R1 of value 10 mm is, for a distance from the opposite convex surfaces of 12.6 mm to focus the rays at the virtual focal spot Fxe2x80x2, at a distance of 50 mm from the external surface of the bottom wall.
the tube comprises an upper external wall, called the upper face, of external surface arranged to reflect the emitted rays back towards the axis of the bore, said external wall being covered with a reflecting material to function in a form called inverted radiation.
The external surface is symmetrical with respect to the longitudinal axial plane of the bore, vertical or perpendicular to the plane to be irradiated, and for example in an arc of a circle or flat;
the tube comprises a reflecting surface securedly united to said tube;
it comprises a reflecting surface for reflection of the emitted rays situated on one side of said tube, a surface comprising two longitudinal side wings symmetrical with respect to an axial plane of the bore, the portion of dioptric or metallic reflecting surface of said side wings being inscribed in a surface of straight or inverted parabolic or appreciably straight or inverted parabolic cross section;
the reflecting surface is formed at least partly by the internal faces of the wings, by dioptric refraction;
the reflecting surface is formed at least partly by a reflecting material;
the tube comprises a bottom external face joining the wings, situated on the opposite side from the generating line at the peak of the tube with respect to the bore.
The face is convex at the centre and appreciably straight at the ends, according to a curve symmetrical with respect to the axial plane containing the generating line at the peak, so as to direct the emitted rays towards a focalization line situated on the irradiation plane.
In the case where the reflecting surface is formed at least partly by two planes symmetrical with respect to the vertical axial plane of the bore, the generating line is replaced by the intersecting line of the flat faces inscribed in a xe2x80x9cchinese hatxe2x80x9d whose upper edge is said intersecting line;
the tube is symmetrical with respect to an axial plane of the bore parallel to the irradiation plane;
the irradiation plane is in general a surface perpendicular to the longitudinal axial plane of symmetry of the tube;
the external wall, or upper face, of the tube is partially cylindrical on the side where the generating line at the peak of the tube is located between the external faces of the side wings;
the upper face of the tube is truncated forming a flat external face between the external faces of the side wings;
the tube is of appreciably cylindrical shape and comprises two added-on glass wings symmetrical or not with respect to the axial plane of the bore perpendicular to the irradiation plane.
In this case, the tube and wings are adjoined, for example simply in contact, or stuck together by a synthetic or ceramic glue, or welded by melting of the quartz, or mechanically fixed to one another;
the bore is formed by four radially distributed glass quarters adjoined via their ends and engaging in a peripheral glass cylinder or a cylindrical bore made in the tube;
the tube comprises a second, cylindrical, tube internal to the bore and designed to contain the plasma bundle and/or containing an emitting filament;
the space between the external tube and the internal tube, adjoined or not to the external tube, can be favourably used for flow of a gaseous or liquid coolant;
the second, cylindrical, tube can be in contact with the generating line at the peak of the convex internal surfaces;
the cylindrical second tube may not be in contact with the convex internal surfaces in so far as the buoyancy created by the internal space of the enclosure bathing in a liquid medium is equal or appreciably equal to the weight of the enclosure, the cylindrical second tube, supported at both ends, then centring itself over its whole length;
the bore comprises an upper surface of concave cross section.
In other words, the top side of the cross section of the bore is concave, i.e. presenting a radius of curvature whose centre is situated on the side of the bore or the peak in the opposite direction to the latter;
the bore is arranged to contain a gas normally ionized under medium or high pressure, the emitted rays being ultraviolet, and/or visible, and/or infrared rays.
By medium or high pressure we mean absolute gas pressures greater than 2 kg/cm2, for example 3 kg/cm2 for a medium pressure and greater than 5 kg/cm2 for a high pressure, able for example to go up to 15 kg/cm2.
the tube comprises electrode chambers of internal section greater than or equal to the internal section of the radiating emitting part of the tube;
the tube comprises an infrared radiation-emitting filament.
A third object of the invention is to achieve an emitter/reflector device implementing one or more tubes as described previously.
Advantageously the device comprises, situated at the focal plane of concentration of the emitted rays, a blade with parallel or appreciably parallel side faces in the form of a funnel, comprising a dioptric radiation input surface able to transform the convergent rays received into a parallel radiation flux.
In an advantageous embodiment, the device comprises reflecting surfaces separated from the tube and constituted by reflecting plates able to be advantageously flat.
A fourth object of the invention also relates to a method for application of rays to a product in sheet form or disposed on a flat or curved surface. It consists in irradiating the product with a radiation-emitting element (plasma bundle or electric filament) presenting a very small cylindrical or appreciably cylindrical cross section, i.e. with a diameter smaller than about 10 mm, for example of about 4 mm, about 2 mm, or even down to 1 mm, and even 0.5 mm (by xe2x80x98aboutxe2x80x99, it must be understood xc2x11 mm and/or 10 to 15%), centred in the bore of a straight glass tube elongate around an axis, said bore being of appreciably square or rectangular shaped cross section at least two opposite sides of which are in the form of convex curves, said sides forming dioptric surfaces arranged to modify the direction of the rays emitted from the axis of the bore to make them parallel or appreciably parallel in the transparent solid medium of the glass, before being diverted to the product by metallic or dioptric reflecting surfaces.
In an advantageous embodiment, the bore comprises four convex sides, the opposite sides being identical two by two.
Advantageously, the emitting element is a tubular plasma bundle emitting ultraviolet and/or visible and/or infrared photon rays.
The tubular plasma bundle of ultraviolet rays preferably has a cross section presenting a maximum radial dimension smaller than or equal to about 4 mm.
The emitting element can be formed by an electric filament, emitting infrared rays.
In an advantageous embodiment, two irradiation planes situated symmetrically on each side of said emitting tube are irradiated with a single tube.